A transportation network is any navigable system of roads, pedestrian walkways, paths, rivers, shipping lanes or other network that is utilized to transport humans or vehicles. A transportation network can also include combinations of routes for the above modes of transportation. These combinations of routes are referred to as multimodal transportation networks. A segment of a transportation network (referred to as a transportation network segment) is a portion of the transportation network that represents a path of travel for a vehicle or pedestrian without a method of entry or exit other than at its end points.
A transportation network can be modelled and stored as a digital representation in a digital map database. In so doing, the transportation network is usually represented as a plurality of navigable segments (or “links”) connected at nodes, with attributes being associated with the links and/or nodes. Nodes are therefore connectors between the links, and generally occur at intersections where there is a decision point with respect to travel from one navigable segment to another. Conventionally, in the context of a transportation network, the attributes limit how travel can flow on the network. For example, attribution may include: geometry, speed of travel, whether or not a turn at an intersection is allowed (i.e. allowable “manoeuvres”), at least one direction of traffic flow, number of lanes, etc.
Typically, such digital maps of transportation networks are created by traversing all paths/elements of the transportation network with highly specialized location measuring and recording systems designed for this purpose. Transportation network information can also be gleaned from aerial images or compiled from existing localized digital transportation networks. It is also becoming more common to create, or at least update and/or refine, a digital map utilizing positional information representative of the movements of one or more, although typically a plurality of, location-aware mobile devices over the transportation network over time.
Such positional information is commonly referred to as “probe data” (or “probe traces”). Each trace indicates a geographic position of each mobile device against time, i.e. traces the path of the device. A location-aware mobile device, herein referred to simply as a mobile device, is any device capable of determining its geographic location from wirelessly received signals. The received signals may include signals received from satellites of a global navigation satellite system (GNSS), such as GPS signals. The mobile device may be a navigation device such as a portable navigation device (PND), in-vehicle navigation device, mobile phone, portable computing device, vehicle tracking device, and the like. The mobile devices may therefore be associated with a vehicle, but it is also envisaged that the mobile devices could be associated with pedestrians. The navigation device is arranged to record a trace of a path or route followed by the navigation device. The navigation device may store the trace in a local memory of the navigation device or may communicate the trace to a server computer, such as via a wireless data connection with the server computer. The trace may be formed from data indicative of a series of geographic locations at which the navigation device is located at periodic intervals. However in other embodiments the trace may be formed by data representing one or more curves indicative of the path of the navigation device.
The methods of creating, updating and/or refining digital maps using probe data can utilise probe traces as received from the mobile devices (often referred to as “uncoordinated” traces), refined probe traces (i.e. uncoordinated probe traces that have been subjected to one or more of the following: smoothing; adjusting the position of at least portions of the trace depending on the direction of traffic flow, filtering traces not associated with a type of the transportation network), one or more bundles each comprising a plurality of traces, or any combination thereof. Bundles of probe traces are formed from a plurality of individual probe traces, uncoordinated or refined, which traverse a path having the same beginning and end within a spatial threshold value and which do not deviate, in location, by more than a threshold from a reference probe trace (e.g. a probe trace passing through a densely populated area of probe traces). In other words, a probe trace bundle is a single probe trace that represents a plurality of individual probe traces; and may be used beneficially in the creation, updating and/or refinement of a digital map.
Despite substantial steps being taken in automating the creation and updating of digital maps, it still remains useful to manually check and validate change requests that may be received. A change request is a message that may originate from a user or which may be automatically generated (e.g. from a comparison of recently received probe data with the current digital map database no) and which indicates a feature of the digital map database no longer matches the real-world transportation network it represents. The change request may, for example, indicate that: a new navigable segment now exists in reality; a navigable segment in the map database no longer exists in reality; the course (i.e. geometry) of a navigable segment has changed; and/or an attribute associated with a navigable segment has changed, such as allowable directions of traffic flow (i.e. a one-way road is now a two-way road), allowable manoeuvres, etc. Once a change request has been validated, i.e. the change indicated in the message has been manually determined to be correct, then the digital map can be updated accordingly.
One way in which individuals can validate a change request is by looking at a visualisation of probe traces, optionally superimposed over a representation of the digital map; thereby showing recent traffic flow for a given road segment or intersection.
Many techniques are known to extract road network characteristics or road network usage from probe, together with ways of visualising such probe traces, including but not limited to traffic density, traffic flow direction, traffic over time analysis and change detection, average speed and road altitude.
It has been recognised, however, that with the amount of traffic flow data that is now received for a given navigable segment or intersection, changes in traffic that may occur on a given road segment or intersection may be difficult to determine. This is particularly the case with determining changes in allowed and/or prohibited manoeuvres at junctions; which is a required feature of the digital map when used to calculate routes from an origin to a destination. This difficulty is illustrated in FIGS. 1 and 2 in which: FIG. 1 shows a density heat map derived from trace data acquired from a plurality of mobile devices; and FIG. 2 shows a traffic flow map data based on trace data acquired from a plurality of mobile devices. An operator responsible for updating map data stored in the digital map database based on one or more change requests to existing map data, for example, map data associated with FIG. 1 and/or FIG. 2 may be delayed in providing the update to the digital map database because the operator may not be able to perceive the requested change because the trace data has not been refined in order to more easily perceive traffic changes.
In view of the foregoing, there is a need for improved methods and systems for determining trajectories through an area over one or more junctions for display from trace data.